Structural effect of polymerisation and dehydration on bolaamphiphilic polydiacetylene assemblies

Abstract

Polydiacetylenes (PDAs) undergo chromic responses to a range of environmental stimuli including temperature, pH and mechanical stress. A novel bolaamphiphilic diacetylene lipid has been synthesized and suspended in aqueous solution as polymerisable micrometer scale assemblies. Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) was used to characterize the structural changes that occurred alongside the blue–red chromic response to dehydration that was observed in these materials after extended UV photo-polymerisation. This revealed a clear correlation between optical properties and molecular structure. Using TEM, the dehydrated polymer samples were found to be anisotropic ribbon-like structures, which were fractured after extended UV exposure, implicating mechanical stress in the chromic transition. FTIR spectra revealed that the chromic transition was also accompanied by significant changes to the molecular structure of the assemblies. These included a disorder–order conformational transition of the pendent alkyl chains and a change to the hydrogen-bonding environment of the amide headgroup. These data provide further insight into the correlation between structure and optical properties of lipid PDA assemblies.